The present invention relates to ignition wire shielding and, in particular, a dissipative cover for grounding spark plug ignition cable electrical charges.
Ignition systems for automotive engines are conventionally provided with an elastomeric boot for covering and protecting the electrical connection between the ignition cable and the spark plug. As engine operating temperatures have increased over the years and as the cylinder heads were located closer to the exhaust manifolds, the temperatures to which the boot and spark plug are exposed have increased correspondingly. The high temperatures reduce the useful life of the boot elastomer, even when high temperature silicone products and protective lubricants are used. In addition, the high voltage ignition systems on current engines can create conditions exceeding the dielectric strength leading to external grounding that can cause further erosion of the boot as well as corrosion of the contact interfaces. It has further been determined that the ignition cables can create high potential gradients, with attendant high E-field intensities creating corona discharges that can further degrade the boots and contacts.
In an early approach, metal shields were used to surround the spark plug boot to shield against excessive heat as disclosed in U.S. Pat. No. 4,497,532 to Benzusko et al. and U.S. Pat. No. 4,671,586 to DeBolt. The shields, however, can provide an adverse grounding path when the dielectric strength is exceeded resulting in engine misfire and performance reduction. It has also been proposed to use high temperature ceramic sleeves to isolate the spark plug boot from high operating temperatures as disclosed in U.S. Pat. No. 6,305,954 to Aluise. The sleeves are rigid and difficult to mount on existing cables, and are limited to in-line boots, to the exclusion of commonplace inclined or right angle boot configurations. The ceramic material does not assist in dissipating electrical fields. It has also been proposed to reduce corona discharge by incorporating a conductive sleeve on the boot interior as disclosed in U.S. Pat. No. 5,716,223 to Phillips et al. All of the foregoing approaches are directed to original equipment limiting the ability to provide improved protection to existing as well as new engines.
It would accordingly be desireable to provide a universal design for ready integration with existing and new ignition cables to protect the boot and electrical connection from deterioration by increasing thermal and radiant insulation, and decreasing adverse electrical effects.
The present invention provides a flexible fabric cover for simple installation over the spark plug boot that is coated with a heat reflective electrical conductive base coat and a dielectric top coat to provide electric dissipation protection. The cover takes the form of currently available fiberglass sleeves having a restrictive mouth that fits over the sparkplug insulator and a sleeve body that covers the boot and connector area and extends therebeyond. The sleeve body has sufficient flexibility to accommodate in-line and angled boots. The base coat comprises a high temperature silicone resin containing electrically conductive aluminum flake that provides infrared reflectivity and a conductive exterior sheath with low break down voltage that dissipates static and corona charges to eliminate elastomer attack. The top coat includes a silicone resin containing a high temperature ceramic pigment effective for providing a dielectric outer coating and increasing thermal resistance. The top coat may include a color pigment for providing an appealing contrasting color to the basically gray/silver coloration of the standard sleeve material. The novel cover may be installed on existing high operating temperature engines to shield against electrical charges, extend life and function of the boot assembly, lower cable operating temperatures. The materials are porous and breathable to reduce heat buildup and reduce moisture retention, non-flammable and non-toxic, and not reactive with petroleum products. The flexible fabric construction allows the cover to be conveniently mounted in recessed plug ports.
Accordingly, it is an object of the present invention to provide an improved cover for protecting spark plug boot assemblies against thermal and electrical degradation.
Another object is to provide a flexible thermal and electrically protective cover for surface mounted and recessed port spark plug boots and connectors.
A further object is to provide a spark plug boot cover that dissipates static and corona charges to reduce degradation and operational impairment of spark plug boots and cable connections.